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Nov. 1, 2011 -- Preterm birth rates improved in nearly every state between 2006 and 2009, but the United States still merited only a "C" on the March of Dimes' latest Premature Birth Report Card.

The U.S. rate rose to a peak of 12.8% in 2006. It declined to 12.3% in 2008 and, according to preliminary data, to 12.2% in 2009.

Back in 1981, the preterm birth rate was 9.4%.

Jennifer Howse, PhD, president of the March of Dimes, attributes the climb over time to such factors as the growing problem of obesity, which increases the risk of gestational diabetes and high blood pressure; increasing numbers of uninsured women; and the rising rate of elective C-sections, some of which may be scheduled too early.

"There have been a lot of trends that have gone in the wrong direction in terms of women's health status," Howse says.

But two went in the right direction between 2008 and 2009, according to the March of Dimes. The percentage of women who smoked, a risk factor for premature delivery, fell from 19.6% to 17.6%, while the percentage of late preterm births, those between 34 and 36 weeks' gestation, inched down from 8.8% to 8.7%.

Births before 37 weeks gestation cost the U.S. more than $26 billion annually, according to a 2006 Institute of Medicine report. It is the leading cause of newborn death, and those who survive often face the risk of lifelong health problems.

The March of Dimes had set a national goal of a 7.6% preterm birth rate by 2010. In this year's report though, the organization announced it had raised the goal for 2020 to a more realistic 9.6%.

"It takes us down 20% from where we are today," Howse says, "but it's a doable goal."

Best and Worst States

With a 9.3% preterm birth rate in 2009, Vermont is the only state to have already reached that 2020 national goal and earn an "A" grade from the March of Dimes.

Mississippi, Alabama, Louisiana, the District of Columbia, and Puerto Rico had the highest preterm birth rates and earned Fs.

Mississippi's rate of 18% was almost double that of Vermont's. Mississippi also has more than twice the rate of uninsured women of childbearing age -- 25% compared to Vermont's 12% -- and higher smoking rates, Howse says.

"Mississippi is a very rural state," says Liz Sharlot, a spokeswoman for the Mississippi State Department of Health. "Access to care is an issue. Poverty is an issue."

Mississippi is in the second and final year of a program designed to lower the state's infant mortality rate, much of which is attributable to Mississippi's high preterm birth rate.

"The whole idea," Sharlot says, "is to ensure that women can get the proper care before they're pregnant, while they're pregnant, and after they're pregnant." In addition, the state is trying to make it easier for pregnant women to sign up for Medicaid.

Whether these efforts are working isn't clear yet, Sharlot says. Mississippi's infant mortality rate declined slightly from 2009 to 2010, but this may not be a significant decrease, she says.